Wow, I can't believe people are still wondering about the dummy thing. Of course the friggin' Infected moved it there.
1.) They specifically introduced that dummy. Hell, I think it was the first one they had Neville interact with in the movie.
2.) I didn't get it from the movie, but from the premise, apparently the Infected are in the business of "watching" Neville during the day from their hideouts. (How they don't know where he lives, then, makes no sense to me. But more on that later.) Therefore the Infected would know (If, of course, they are smart enough to come to conclusions and they would have to be if they did set that trap up) that Neville was fond of that specific dummy.
3.) The SAME friggin' Infected was standing there with those dogs. Now, I knew from the SECOND I saw that thing stick it's face out into the sun that he was going to be a big part of this movie. This is part of the reason why they went to the trouble of showing this cat stick his face out there to get burnt. So you understand the dummy scene. Neville fell for his own trap idea.
Now... How the hell DID the Infected know where he lives? Like I said earlier, you'd figure if they were always watching him (as the premise alludes) then surely one of those days they'd see him go in his house. But he seemed pretty confident they didn't know where he lived and when the girl was driving him home, he even told her to wait until dawn to go to the house, because the Infected didn't know where he lived.
Only part I'm iffy about. Maybe I missed something. After Sam died I kinda started to lose interest.